He appears to mask his rude demeanor and negativity towards others with a calm, timid personality. In other words, he's good at deceiving people. Yamana Akane describes him to be scary looking.
When he was 11 years he was brought to Sun Garden and into Kira Hitomiko's care. It was Hitomiko who sent Kariya into Raimon thought at the start Kirino thinks he might be a Seed from Fifth Sector. To make Kirino mad he says its true that his a Seed. Later Kirino realizes it was a lie and that Kariya is just like the others on the team.
Kariya is a first year and a defender on Raimon's team.